(microsoft powerpoint - seminarium g\366teborg cbi.pptx)

$: (Microsoft PowerPoint - Seminarium G\366teborg CBI.pptx)$
Beständighet av cement och betong i tunnelmiljö

Elisabeth Helsing, Urs Mueller

CBI Betonginstitutet AB, Borås

SeminariumVatten i anläggningsprojekt

Göteborg 2013-11-27

Introduction

Types of cementitious materials for tunnels

Sprayed concrete

Precast concrete

In place casted concrete

Grouting material

�Portlant cement based grouts for consolidating cracks

�Sprayed concrete for stabilizingtunnel walls or as final lining

�Precast elements for linings

� In-situ cast concrete for linings, inverts or instalations (e.g. air ventshafts, paving, drainage)

Vatten i anläggningsprojekt Göteborg 2013-11-27

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General factors

3Vatten i anläggningsprojekt Göteborg 2013-11-27

Material Environment

Amount ofbinder/aggregate

w/c ratio

Binder type

Aggregate type

Air void content

Quality control ofconcrete

Application ofconcrete

Temperture

Moisture content

Ground watercomposition

Tunnel maintenance

Type of surrounding ground/bedrock

Sea water influx

Intended use

Reinforcement

Introduction

Exposure environments in tunnels�Exposure environment is defined by exposure classes

XF3/XF4XD1-XD3

XS2/S3

sea waterCl-

XA1-XA3

ground waterSO4

2-, Mg2+

XC3/XC4

frost, Cl-

CO2 e.g. fromexhaust

� For tunnels in Sweden:

• Frost exposure: XF3/XF4

• Exposure to CO2: XC3/XC4

• Exposure to chloride from sea water: XS2/XS3

• Exposure to chlorides from deicing salts: XD1-XD3

• Exposure to harmful ionsother than chloride (e.g. Mg2+, SO4

2-): XA1-XA3

Vatten i anläggningsprojekt Göteborg 2013-11-27

4

General factors

Damage mechanisms possible in tunnels� Frost attack

�Corrosion of reinforcement induced by chloride from

• sea water

• deicing salts

�Carbonation of concrete due to

• bicarbonate exposure from ground water

• CO2 from traffic exhaust in road tunnels

�External sulfate attack from

• ground water

• sulfide/sulfate containing bedrock/ground

�Alkali aggregate reaction (AAR): Reaction of aggregate with alkalis in pore solution of the concrete


Damage processes

Example: External sulfate attack� The hydrate phase calcium aluminate monosulphate hydrate

(monosulphate) in the cement paste can react with external sulfate, which penetrates the concrete


air void

cement paste

aggregate

monosulfate

formation of ettringite by reaction with sulfate and moisture expansion

after Famy et al., 2004

SO42-

SO42-

SO42-

SO42-

Damage processes

Example: External sulfate attack� The reaction product of monosulfate with external sulfate is

ettringite, which has a ca. 2.2 times higher volume� expansion of cement paste


cracks + voids filled

with ettringite

expansion and re-crystallization

Damage processes




cracks + voids filled with ettringite

Damage processes



�As a consequence the concrete starts to crack and looses strength

� In tunnel linings damages start usually on the interface between lining and rock if sulfate comes from ground water


Prevention of damages

Strategies for preventing sulfate attack�Application of European standards and national standards/rules

for preparation of concrete

• Apply requirements for respective exposure class and additional national requirements

�Use of sulfate resistant cement (Portland cement low in Al2O3 or adequate composite cements, e.g. CEM III)

�Avoidance of limestone fillers or composite cement with a higher amount of limestone � minimizing the risk of Thaumasite formation

�Sulfate attack of concrete in Sweden in tunnel environment is rare

• Only few cases with very old concrete

• Strategy with using sulfate resistant cements for most tunnels seem to work



Strategies for preventing sulfate attack�Sulfate attack of concrete in tunnel environment is less frequent if

standards and rules were applied

• Only cases with concrete > 50 a show sulfate attack, in newer concrete very rare

• In Sweden strategy with using sulfate resistant cements for most tunnels seem to work



Strategies for preventing other damage�ASR

• Caused by reaction of aggregate with alkalis in the concrete


cracked aggregate cracked concrete cracked structure


Strategies for preventing other damage�ASR

• Control of ASR reactivity of aggregate used in tunnel environment � ASR tests according to RILEM AAR-1 to -4

• Use of low alkali binder systems

�Reinforcement corrosion due to chloride/carbonation

• Reduction of capillary porosity of concrete � reduction of ion diffusivity

� Frost

• Increase of air void content

�Overall

• Enforce strict quality control concerning concrete quality and its application



EN/Swedish standards and guidelines concerning durability aspects for concrete in tunnels


And many more…


EN/Swedish standards and guidelines concerning durability aspects for concrete in tunnels�EN 206 and SS 137003 (Betong - Användning av EN 206-1 i

Sverige)� General concrete standards

�Sprayed concrete

• SS EN 14487-1:2005 Sprutbetong - Del 1: Definitioner, specifikationer och kriterier för överensstämmelse

• SS EN 14487-2:2006 Sprutbetong - Del 2: Utförande

�E.g. Trafikverket

• AMA/TRVAMA Anläggning 10

• TRVK Tunnel 11 Trafikverkets tekniska kravTunnel TRV publ nr 2011:087


Conclusions

• Damage risks for concrete in tunnels can be minimized by applying current standards and rules

• A challenge poses newer binder systems, where only limited long term experience exists

• Here, there is a need for more research and an exchange in experience with other countries


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